Weekly seminars with guest speakers.
Thursdays 9:00AM - 10:00AM Tech M345
Simon Rogers
UIUC
Host: Jeff Richards
Title: A material’s perspective: Developing a transient framework for understanding nonlinear rheological responses
Abstract: Modern society relies on soft materials, which are important for foods, consumer products, biological materials, and energy and environmental applications. The interactions that hold soft materials together are often comparable in magnitude to the thermal energy, making them especially susceptible to weak forces. In order to develop functional soft materials, they need to be processed far from equilibrium. Despite recent progress, we still do not understand how molecular-scale behavior informs macroscopic properties in these systems. Of particular interest is the transient rheology, where stresses and deformations can induce massive molecular reorganizations that manifest as transformations in the macroscopic material properties. Transient conditions are encountered in most biological situations, and well as industrial flows including startup and cessation, which often dictates the success of a product or process.
The overwhelmingly preferred method for probing the viscoelasticity of soft materials is the application of oscillatory shearing, in which a material is sinusoidally deformed. When the amplitude of the shearing is small, the responses elicited are also sinusoidal. These responses are typically decomposed into components in-phase and an out-of-phase with the deformation to obtain the dynamic moduli, G’ and G”. When the experiment is extended to mirror more realistic processing conditions by increasing the amplitude of the deformation, the response of the material being tested becomes non-sinusoidal. There has been a significant effort in the last decade to develop methods capable of providing clear physical insight into nonlinear responses. Many of these schemes, such as Fourier transformation, take linear algebraic approaches and describe an entire period of oscillation in terms of some orthonormal basis. However, the typical phenomenological descriptions of nonlinear responses use the language of sequences of processes, and not linear summations. This is evident in a number of recent studies that have identified features in the nonlinear oscillatory responses of colloidal glasses and gels that are best described from the perspective of the material in terms of elastic deformation followed by yielding, and then stable flow.
In this talk, I will present a new quantitative framework for understanding nonlinear transient rheological responses that is commensurate with the phenomenological studies and physical descriptions. The new approach describes responses in terms of instantaneous measures that are well-defined everywhere. I will show the results of new experiments that are inspired by the new quantitative framework that clearly link molecular-level information to the macroscopic rheology, providing a rational route toward structure-property-processing relationships.
Bio: Simon A. Rogers is an Assistant Professor in the Department of Chemical and Biomolecular Engineering at the University of Illinois at Urbana-Champaign. Dr. Rogers uses experimental and computational tools to understand and model advanced colloidal, polymeric, and self-assembled materials. He joined the department in 2015. He received his BSc in 2001, BSc (Hons) in 2002; and his PhD from Victoria University of Wellington in New Zealand in 2011. He completed his postdoctoral research at the Foundation for Research and Technology in Crete, the Jülich Research Center in Germany, and the Center for Neutron Research at the University of Delaware.
Cost: Free
Elizabeth Rentfro
(847) 491-2773
Email